I have a 3.7, 3.9 and a 4.22.
I'm not letting go of any of 'em.
I am still needing to reassemble the ribcase with the prefered 1275 gears
back into one piece.
I'm still debating whether or not I will stick in the 3.7 or the 4.22 diff
in the axel when putting the rest of the car back into one piece. One of
these years.
I had the 3.9 in there. It was fine. The 4.22 was the original when the
948 was in the car (Which I still have). The 3.7 would be interesting.
I too have often wondered how the car will take off from 1st gear with the
3.7. I have often wondered how much fun it will be buzzing around with the
4.22.
Seen as I work 3 miles from where I live, and only drove in very short
distances throughout the dense residential neighborhood, I'm better off
going with the 4.22.
Who out here has a 3.7 hooked up with a 1275/ribcase combo? And how does
it work?
Q
At 04:24 PM 10/21/97 -0700, Ulix Goettsch wrote:
>CAUTION: I am going for the most-boring-post award with this one.
>
>The Spridget came with three different rear end ratios.
>1:4.22 until 1967 I think
>1:3.9 from 1967 to 77 or 78 I think (I should look this up)
>1:3.7 from 77/78 to the end of production
>
>I have been thinking about swapping out my rear end (no jokes here!) for a
>lower ratio one (lower rpm on the highway) but was concerned about
>off-the-line response around town. Here are my conclusions.
>
>My car is one of the last to have the 4.22 ratio which made for high rpm
>on the highway. I installed the 5-speed conversion which has a 5th gear
>ratio of 1:0.821 (stock 4th is 1:1). So the speed that I used to achieve
>at 5000rpm (whatever speed that may be), I now achieve at 4100rpm. If I
>swap in a 3.9 rear end, I will achieve the speed at 3800rpm. A 3.7 would
>yield 3600rpm. Sounds great!
>
>But making this change will also be noticed in a "longer" 1st gear, making
>take-off from a stop more sluggish. Fortunately, the 1st gear in the
>Datsun trans is "shorter" than the one in the ribcase, partially
>offsetting this effect:
>
>1st gear ratio:
>Ribcase 3.2:1
>Datsun 3.513:1
>
>So I calculate an effective rear end ratio. Using a 3.7 rearend with a
>Datsun trans will have the same overall 1st gear ratio as using a rearend
>ratio of 4.06 with a ribcase box. Since 4.06 is between 4.22 and 3.9, the
>two ratios used with the 1275 cars, I shouldn't have any problem
>starting up on steep Seattle hills!
>
>By now, Larry Miller is probably the only one still reading (he wondered
>about this too), but for completeness some more facts.
>Using a 3.9/Datsun combination yield an effective ratio of 4.28, almost
>exactly what I started out with (4.22).
>
>To calculate how much a rearend change would help you (even our ribcased
>friends), take the rpm you usually run on the interstate, devide by your
>current ratio, then multiply by the 'new' ratio.
>
>You could also calculate how much faster you could go at the same rpm by
>taking your current highway speed, times your current ratio, devided by
>your new ratio - however, you probably don't know how fast you are going
>anyway because your speedo needle is fluttering back and forth, it doesn't
>move at all, or it is inaccurate.
>
>One more note of caution, the 3.7 was only used in the 1500 Midgets which
>have more torque and a 'shorter' 1st gear of 3.41. So an earlier Spridget
>with a ribcase box might not like this 'long' rearend.
>
>OK, so who has a 3.7 for sale (cheap?)...
>
> Ulix __/__,__
>.......................................................... (_o____o_)....
> '67 Sprite
>
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